1. Field of the Invention
The present invention relates to additive compositions for use as rust inhibitors in liquid media coming into contact with ferrous metals. More particularly, the invention is concerned with rust inhibitor additives which are capable of being stably dispersed, or soluble, in aqueous media.
2. Description of the Prior Art
It is well known that ferrous metal surfaces tend to rust soon after coming into contact with water. The tendency of the metal surface to rust is especially noticeable in metal cutting or metal working operations. In such operations the freshly cut or worked surface is very susceptible to rusting (oxidation) by water, moisture or aqueous media. For economic reasons, aqueous solutions or fluids including aqueous emulsions have been used extensively as both lubricants and coolants in many ferrous metal cutting operations. One major concern with such aqueous fluids is how to best minimize or eliminate their otherwise severe rusting and corroding effects on ferrous metal surfaces. Thus, an effective rust inhibitor has always been a must additive to any of the foregoing aqueous media.
A host of rust-inhibitor additives in aqueous media have been proposed in the prior art. Such additives have comprised phosphate esters, phosphate esters adducts with ethylene oxide and phenol, salts of aromatic acids such as benzoic, toluic, naphthoic, phthalic acid with aliphatic amines, nitrous acid salts of long chain aliphatic amines such as the nitrous acid salt of octadecylamine, or salts of aromatic sulfonamidocarboxylic acids. Other known rust-inhibitors also include those additives formed from combining metal salts with alcohols or amines; graphite, borax, clay, and silica-containing compounds; and condensation products of alkali metal or alkaline earth metal borate with polyhydric alcohols.
One particularly effective rust-inhibitor additive has been sodium nitrite. The fact that sodium nitrite is water-soluble, commercially available, and easy to use has assisted in its wide acceptance as a rust inhibitor in aqueous cutting fluids. Recent findings, however, have made use of sodium nitrite in cutting fluids undesirable and possibly hazardous. Apparently, at elevated temperatures sodium nitrite reacts with organic amines, often found in cutting fluids, to form nitrosoamines which are suspected as potential carcinogenic materials.
Efforts have been extensive to prepare rust inhibitor additives which are safe yet as equally effective in aqueous systems as sodium nitrite.
It is therefore the primary object of the present invention to provide novel compositions for inhibiting the rusting of ferrous metal surfaces in contact with water or aqueous solutions.
Another object of the invention is to provide novel aqueous industrial fluids which have rust-inhibiting properties and novel concentrates for preparing the same. A further object of the invention is to provide a novel method for metal working, and especially metal cutting, wherein a novel aqueous industrial fluid having anti-rust properties is utilized. Other objects and advantages will become apparent from the following descriptions.